Thermoelastic properties of α\alpha-iron from first-principles

We calculate the thermomechanical properties of $\alpha$-iron, and in particular its isothermal and adiabatic elastic constants, using first-principles total-energy and lattice-dynamics calculations, minimizing the quasi-harmonic vibrational free energy under finite strain deformations. Particular care is made in the fitting procedure for the static and temperature-dependent contributions to the free energy, in discussing error propagation for the two contributions separately, and in the verification and validation of pseudopotential and all-electron calculations. We find that the zero-temperature mechanical properties are sensitive to the details of the calculation strategy employed, and common semi-local exchange-correlation functionals provide only fair to good agreement with experimental elastic constants, while their temperature dependence is in excellent agreement with experiments in a wide range of temperature almost up to the Curie transition.Comment: Accepted as regular article in Phys. Rev.

Energetics and thermodynamics of α-iron from first-principles and machine-learning potentials

Iron is a material of fundamental importance in the industrial and economic processes of our society as it is the major constituent of steels. With advances in computational science, much progress has been made in the understanding of the microscopic mechanisms that determine the macroscopic properties of such material at ordinary or extreme conditions. Ab initio quantum mechanical calculations based on density-functional theory (DFT), in particular, proved to be a unique tool for this purpose. Nevertheless, in order to study large enough systems up to length- and time-scales comparable with those accessible in experiments, interatomic potentials are needed. These are typically based on functional forms driven by physical intuition and fitted on experimental data at zero/low temperature and/or on available first-principles data. Despite their vast success, however, their low flexibility limits their systematic improvement upon database extension. Moreover, their accuracy at intermediate and high temperature remains questionable. In this thesis, we first survey a selection of embedded atom method (EAM) potentials to understand their strengths and limitations in reproducing experimental thermodynamic, vibrational and elastic properties of bcc iron at finite temperature. Our calculations show that, on average, all the potentials rapidly deviate from experiments as temperature is increased. At the same time, they suggest that, despite an anomalous rapid softening of its $C_{44}$ shear constant, the Mendelev03 parameterization is the most accurate among those considered in this work. As a second step, we compute the same finite-temperature properties from DFT. We verify our plane-wave spin-polarized pseudopotential implementation against selected zero temperature all-electron calculations, thus highlighting the difficulties of the semi-local generalized gradient approximation exchange and correlation functional in describing the electronic properties of iron. On the other hand, we demonstrate that after accounting for the vibrational degrees of freedom, DFT provides a good description of the thermal behavior of thermodynamic and elastic properties of $\alpha$-iron up to a good fraction of the Curie temperature without the explicit inclusion of magnetic transverse degrees of freedom. Electronic entropy effects are also analyzed and shown to be of secondary importance. Finally, we attempt at generating a set of highly flexible Gaussian approximation potentials (GAP) for bcc iron that retain ab initio accuracy both at zero and finite temperature. To this end, we use a non-linear, non-parametric Gaussian-process regression, and construct a training database of total energies, stresses and forces taken from first-principles molecular dynamics simulations. We cover approximately $10^5$ local atomic environments including pristine and defected bulk systems, and surfaces with different crystallographic orientations. We then validate the different GAP models against DFT data not directly included in the dataset, focusing on the prediction of thermodynamic, vibrational, and elastic properties and of the energetics of bulk defects

Assessing and Improving Flood and Landslide Community Social Awareness and Engagement via a Web Platform: The Case of Italy

Italy is significantly affected by ever-present flood and landslide risks and has experienced many disasters. Local social awareness and engagement, however, differ and need to be increased by decision makers and citizens through improvements in risk preparedness. With this aim, the #italiasicura web platform was developed by Fondazione Politecnico di Milano and released in 2015 to show country to local level hazard maps and risk reduction projects in Italy. Any stage of the user experience with the platform can be shared via social media. Using this tool, an awareness-oriented web analytics process was structured to develop a set of indicators for the increase of knowledge linked to flood and landslide hazards. In so doing, it is possible to measure community disaster awareness actions and competence in the area of hazard knowledge. This article presents the results obtained by using data from the platform

Thick Does the Trick: Genesis of Ferroelectricity in 2D GeTe-Rich (GeTe)m (Sb2 Te3 )n Lamellae

The possibility to engineer (GeTe)(m)(Sb2Te3)n phase-change materials to co-host ferroelectricity is extremely attractive. The combination of these functionalities holds great technological impact, potentially enabling the design of novel multifunctional devices. Here an experimental and theoretical study of epitaxial (GeTe)(m)(Sb2Te3)n with GeTe-rich composition is presented. These layered films feature a tunable distribution of (GeTe)m(Sb2Te3)(1) blocks of different sizes. Breakthrough evidence of ferroelectric displacement in thick (GeTe)m(Sb2Te3)(1) lamellae is provided. The density functional theory calculations suggest the formation of a tilted (GeTe)m slab sandwiched in GeTe-rich blocks. That is, the net ferroelectric polarization is confined almost in-plane, representing an unprecedented case between 2D and bulk ferroelectric materials. The ferroelectric behavior is confirmed by piezoresponse force microscopy and electroresistive measurements. The resilience of the quasi van der Waals character of the films, regardless of their composition, is also demonstrated. Hence, the material developed hereby gathers in a unique 2D platform the phase-change and ferroelectric switching properties, paving the way for the conception of innovative device architectures

Rates of adverse events in patients with ulcerative colitis undergoing colectomy during treatment with tofacitinib vs biologics : a multicenter observational study

Three hundred one patients (64 tofacitinib, 162 anti-tumor necrosis factor-a agents, 54 vedolizumab, and 21 ustekinumab) were included. No significant differences were reported in any outcome, except for a higher rate of early VTE with anti-tumor necrosis factor-a agents (P 5 0.047) and of late VTE with vedolizumab (P 5 0.03). In the multivariate analysis, drug class was not associated with a higher risk of any early and late complications. Urgent colectomy increased the risk of any early (odds ratio [OR] 1.92, 95% confidence interval [CI] 1.06–3.48) complications, early hospital readmission (OR 4.79, 95% CI 1.12–20.58), and early redo surgery (OR 7.49, 95% CI 1.17–47.85). A high steroid dose increased the risk of any early complications (OR 1.96, 95% CI 1.08–3.57), early surgical site complications (OR 2.03, 95% CI 1.01–4.09), and early redo surgery (OR 7.52, 95% CI 1.42–39.82). Laparoscopic surgery decreased the risk of any early complications (OR 0.54, 95% CI 0.29–1.00), early infections (OR 0.39, 95% CI 0.18–0.85), and late hospital readmissions (OR 0.34, 95% CI 0.12–1.00).peer-reviewe

First-Principles Study on the Crystalline Ga4Sb6Te3 Phase Change Compound

The compound on the pseudobinary tie‐line is proposed in the literature as a phase change material with high crystallization temperature. Herein, the crystal structure of this compound is uncovered by means of a genetic algorithm and electronic structure calculations based on density functional theory. As opposed to the parent GaSb compound which crystallizes in the zincblende structure, the compound features an octahedral‐like coordination for Ga as well as for Sb and Te atoms. Other structures close in energy to the ground state are also proposed, including some with a tetrahedral‐like coordination of Ga atoms. Raman spectra computed within density functional perturbation theory and an empirical Bond Polarizability Model are shown to be able to discriminate among the different possible local environments of Ga atoms

Antioxidant properties of propargylamine derivatives: assessment of their ability to scavenge peroxynitrite

A series of arylpropargylamines, variously substituted in the hydrogen in p-position and in the propargyl moiety, were studied as potential peroxynitrite scavengers. The scavenging activity of these compounds was evaluated through peroxynitrite (ONOO-)-mediated oxidation of dichlorofluorescin and linoleic acid by measuring the dichlorofluorescein formation and oxygen consumption, respectively. Among tested compounds, only 1-phenylpropargylamine (AP3) promoted concentration-dependent inhibition of ONOO(-)-induced dichlorofluorescin and linoleic acid oxidation with IC50 values of 637 and 63 microM, respectively. The AP3 spectral changes in UV-visible absorbance properties in the presence of peroxynitrite suggested the formation of a new compound. This was identified by gas-chromatograph-mass spectrometer analysis as phenylpropargyl alcohol. Structure-activity relationship analysis indicated that the scavenging activity of AP3 was due to the aminopropargyl moiety and availability of the nitrogen electron pair. This data suggested that AP3 could be considered a lead compound for the synthesis of new ONOO- scavenger derivatives

A noise-robust obstacle detection algorithm for mobile robots using active 3D sensors

none5Obstacle detection is one of the most important tasks for mobile robots moving along a plane, and it is critical to avoid damages, either to the robot or to human operators. In the past decades, several techniques were proposed for visual navigation of mobile robots, relying on different kind of sensors and algorithms: sonar sensors, laser stripes, and stereo vision are commonly used techniques. Even if these techniques are well-established and used in commercial robots, different and better sensors are now widespread, such as depth sensors. This work proposes an algorithm based on the use of an active 3D depth sensor for obstacle detection and avoidance. The algorithm, conceived to be used in embedded systems with low processing power, underwent several experiments and proved to be robust to Gaussian white noise.Andrea Claudi;Daniele Accattoli;Paolo Sernani;Paolo Calvaresi;Aldo Franco DragoniClaudi, Andrea; Daniele, Accattoli; Sernani, Paolo; Paolo, Calvaresi; Dragoni, Aldo Franc